This application is based upon and claims priority from prior French Patent Application No. 0108192, filed Jun. 21, 2001, the disclosure of which is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention generally relates to a process for treating complementary regions of the surface of a substrate and to a semiconductor product thus obtained by this process. More particularly, the present invention the field of fabricating semiconductor products and its applications lie in particular in the treatment of substrates by different treatment steps on complementary regions of their surfaces.
2. Description of Related Art
The term xe2x80x9csubstratexe2x80x9d is used to denote a support, which has possibly already received various treatments of varied kinds and intended to receive at least one additional treatment. The surface of this support is in general plane or approximately plane in order to be able to use the usual treatment tools and methods for plane surfaces in the field of the fabrication of semiconductor products. These tools and methods possibly being adapted in the case of surfaces which are not strictly plane, for example using devices for the development of a cylindrical surface.
The term xe2x80x9csemiconductor productxe2x80x9d is used to denote a substrate intended in its final application to support electronic components. This is therefore in general a semi-finished product appearing in the course of the fabrication of a number of components carried by a single support.
The surface treatments considered by the invention may be of very varied kinds, for example implantation of atomic or ionic species, deposition of chemical species, etching, treatment of the surface using a physical principle, especially by bombardment or irradiation, surface treatment according to a chemical principle, especially by surface reaction or by sensitization, and more. The feature of the surface treatments relating to the invention is the need for direct access to the region of the surface to be treated, possibly access by exposure of this exposed region, access by contact, especially for contacting with a liquid solution, and other surface treatments. One particularly widely used surface treatment is the implantation of arsenic or phosphorus into a silicon substrate in order to impart n-type semiconductor behavior on it, or the implantation of boron or boron fluoride in order to impart p-type semiconductor behavior on it. More generally, the two surface treatments of the regions of the first group of regions and of the second group of regions are, respectively, two treatments of the substrate by implantation of atomic or ionic species so as to create two different dopings.
As a matter of fact, in the above technical field, it is frequently the case to have to apply different treatments to complementary regions of the surface of a substrate. This occurs when a first group of regions has to receive a first surface treatment, while a second group of regions has to receive a second surface treatment, without the first or the second regions being subjected to the effects of the surface treatment intended for the other region.
The expression xe2x80x9cgroups of complementary regions with respect to the surface portion of the substratexe2x80x9d is understood to mean that this surface portion is divided into two groups of regions so that joining the regions of these two groups of regions reconstitutes the initial surface portion of the substrate in its entirety and without any overlap of parts of regions. The selective exposure of the regions of a group of regions to a surface treatment which is intended for it without the regions of the other group of regions being subjected to the effects of this surface treatment requires placing, on the latter regions, one or more screen layers capable of blocking the effects of the treatment on the substrate surface thus protected. Since the two groups of regions have to receive a respective surface treatment exclusively with respect to the regions of the other group of regions, two steps of depositing screen layers are necessary, successively on the regions of each of the two groups of regions, before the surface treatment intended for this group of regions is applied.
These screen layers must therefore leave exposed the regions that have to receive the effects of the surface treatment which is intended for them. Their depositions must therefore be selective, this selectivity resulting from the use of respective specific masks, which differentiate the regions of one of the two groups of regions with respect to those of the other group of regions. Each mask is positioned with respect to the substrate with a precision of about 0.10 to 0.18 xcexcm, using identification marks for aligning the mask with respect to the substrate, and with a procedure consisting of several repeated steps of progressively readjusting the position of the mask. According to the existing methods, these operations of positioning the mask are carried out during each deposition of the screen layers, that is to say at least twice in the case considered here of two different surface treatments applied to two groups of complementary regions of the substrate surface.
However, the imprecision in positioning the aforementioned masks prevents the regions of one group of regions being contiguous with regions of the other group of regions, that is to say there is a residual substrate band between the regions of each group of regions which is either not subjected to either the first or the second treatment, or is successively subjected to the effects of both surface treatments. This results, in the first case, in the formation of parts of the surface of the substrate which are not treated, and therefore lost from the standpoint of the fabrication of electronic circuits. Furthermore, a substrate band which is not treated by any of the two surface treatments is in an uncontrolled electrical state which may affect the subsequent operation of the electronic circuits. This is particularly so for a pure silicon substrate when the two surface treatments consist of implantations of doping species defining the electrical behavior of the implanted regions. In the second case, this results in the formation, between regions belonging to different groups of regions, of substrate bands receiving successively both surface treatments. Such regions are also deleterious, for the same reasons as those mentioned above, in particular in the aforementioned case of doping treatments of a pure silicon substrate. Accordingly, a need exists to overcome the problems of a xe2x80x9cresidual substrate bandxe2x80x9d and to provide a product and process with little or no xe2x80x9cresidual substrate band.xe2x80x9d
One object of the present invention is to provide a process which comprises the use of only a single mask for carrying out two different surface treatments intended for separate regions, and therefore comprising only a single operation of positioning the mask with respect to the substrate.
The invention relates more particularly to a process for treating a surface portion of a substrate comprising a first group of regions intended to receive a first surface treatment and a second group of regions intended to receive a second surface treatment different from the first surface treatment, the two groups of regions each comprising at least one region and being mutually complementary with respect to the surface portion, wherein:
a step of selectively protecting the regions of the second group of regions against the effects of the first surface treatment is carried out by the selective deposition of at least one layer formed from first materials on the regions, using a mask which differentiates the regions belonging to the first group of regions from the regions belonging to the second group of regions;
the first surface treatment is applied so that it has an effect only on the regions of the first group of regions;
a step of selectively protecting the regions of the first group of regions against the effects of the second surface treatment is carried out by the deposition on the surface portion of at least one layer formed from second materials and by selective removal of the layers for protecting the regions of the second group of regions against the effects of the first surface treatment so that protection layers remain only on the regions of the first group of regions, this selectivity being obtained by alternating the steps of removing these layers with the steps of depositing the materials causing the regions of the first group of regions to be protected against the effects of the second surface treatment; and the second surface treatment is applied so that it has an effect only on the regions of the second group of regions.
The fact of using only a single mask has the advantage of reducing the number of steps of the overall process and also of reducing the number of machines needed for this process, the cycle time and therefore the overall cost of this process.
This process may be continued using the same logic, on the basis of the initial differentiation between the two groups of regions, that is to say without reusing the mask for differentiating the regions of the two groups of regions, for the purpose of applying a third surface treatment to the regions of the first group of regions, and against the effects of which treatment the same protective materials as those already used provide effective protection of the substrate. Thus, protection of the regions of the second group of regions may be reconstructed from protection layers, while removing the protection layers from the regions of the first group of regions using the same removal steps alternating with the steps of depositing the protective materials on the regions of the second group of regions. The third surface treatment may therefore be applied so that it has an effect on the regions of the first group of regions. This sequence of steps may again be repeated without limit, in order to carry out surface treatments having an alternating effect on the regions of each of the two groups of regions without having an effect on the regions of the other group of regions, no loss of definition of the two groups of regions occurring during this sequence.
According to the process of the invention, the selective protection of the regions of each respective group of regions against the effects of the surface treatment intended for the regions of the other group of regions is obtained by at least one screen layer and at least one screen protection layer. These layers are obtained from respective materials which are deposited separately on the surface portion of the substrate. During the rest of the process, the screen layer forms, for the underlying region, a screen against the effects of the treatment intended for the regions of the other group of regions, and the screen protection layer protects the underlying screen layer against a process for removing the screen layer.
Advantageously, the screen protection layer used is also photosensitive and capable of being developed. It is therefore irradiated at the start of the process after the deposition of the materials causing the regions of the second group of regions to be protected against the effects of the first surface treatment, this irradiation being carried out using the mask which differentiates the regions of the first group of regions from the regions of the second group of regions. According to the invention, the subsequent depositions of screen protection layers no longer use irradiation and development steps to provide the selective protection of the regions of a group of regions, but this selectivity is obtained by using the protection layers already present on the regions of the other group of regions.
To do this, after application of the first surface treatment, the deposition of the new screen and screen protection layers is carried out during successive steps alternating with steps of selectively removing the layers for protecting the regions of the second group of regions against the effects of the first surface treatment.
This selective removal of the layers for protecting the regions of the second group of regions against the effects of the first surface treatment comprises at least one step of mechanical abrasion, or dry etching, or planarizing etching, or dissolution, or chemical etching.
This selective removal is controlled in its progressive advance towards the surface of the substrate with respect to the removal of the screen protection layer present above the regions of this second group of regions. Several methods are possible for this control; in particular, analysis of the material residues removed can provide, as identifying mark, a change of chemical composition of these residues by passing from one screen material layer at the end of removal to a screen protection layer starting to be removed, or vice versa.
According to another method of controlling the progress of the removal steps, the screen protection layers possess a first state or a different second state, the second state giving the screen protection layer the property of greater resistance to the process of removing the protection layers compared with the resistance of the screen layers to the removal process. The progress of the removal of the successive layers can then be monitored by timing, or else, in the case of removal by abrasion using a rotating disk, by monitoring the torque of this disk, this torque being greater when the abrasion relates to the screen protection layer.
In another embodiment, the residues produced during the mechanical polishing such as by a rotating disk are analyzed. The residue produced from the screen protection layer is chemically different than the residue produced from polishing the screen layer.
To do this, the screen protection layers pass from their first state to their second state by a treatment applied in situ. Since this treatment has the effect of xe2x80x9chardeningxe2x80x9d the material of this screen protection layer, it is preferably carried out after the removal of the material or materials constituting the screen protection layer from the regions that have to receive the effects of the next surface treatment.
The invention also relates to a process for obtaining a semiconductor product comprising steps of carrying out a process for treating a substrate, such as those described above.
Moreover, the invention relates to the semiconductor product treated or obtained according to the process of the invention or to this process for obtaining the product. Such a product therefore possesses contiguous regions that have undergone different respective treatments specific to each group of regions. In the case of implantation treatments, the contiguity of the regions thus treated may be revealed by elemental analysis and in the case of other treatments this contiguity may especially be observed by scanning electron microscopy. The formation of wells of opposite, p and n, doping types in contiguous and alternating regions arises especially in the fabrication of transistor memories requiring a large number of transistors produced on the same support with a maximum density. Other electronic components, such as processors, also benefit in their fabrication from the advantages of the present invention, especially so as to increase the manufacturing precision and the miniaturization of the circuits which contain them.